Thin polished plates such as silicon wafers and the like are a very important part of modern technology. A wafer, for instance, may refer to a thin slice of semiconductor material used in the fabrication of integrated circuits and other devices. Other examples of thin polished plates may include magnetic disc substrates, gauge blocks and the like. While the technique described here refers mainly to wafers, it is to be understood that the technique also is applicable to other types of polished plates as well. The term wafer and the term thin polished plate may be used interchangeably in the present disclosure.
Fabricating semiconductor devices typically includes processing a semiconductor wafer using a number of semiconductor fabrication processes. For example, a wafer can have a top layer polished or a top layer just formed from certain chip production processes. A semiconductor fabrication process known as lithography may then transfer a pattern from a reticle to a resist arranged on the semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Generally, certain requirements may be established for the flatness and thickness uniformity of the wafers. There exist a variety of techniques to address the measurement of shape and thickness variation of wafers. However, most existing wafer measurement tools are designed for bare wafer geometry measurements. Their abilities to provide useful pattern structure information of patterned wafers are limited.